1. Field of the Invention
This invention relates generally to a storage medium and more particularly to a method and apparatus for accessing the same.
2. Description of the Prior Art
Magnetic memory, such as magnetic random access memory (MRAM), shows exciting potential as the future's favorite memory in a wide variety of applications. This is arguably mostly attributable to manufacturing limitations faced by currently-popular memory, such as dynamic random access memory (DRAM) and static random access memory (SRAM). Such limitations include volatility of these memories. These devices will only hold their contents while power is being applied and loss their contents when power is removed. For example, current applications of non-volatile dual in-line memory module (NVDIMM) in the marketplace incorporate DRAM in addition to some sort of backup system such as batteries, super capacitors or a network of Tantalum caps, a PLD, power monitoring system, and non-volatile backup media such as NAND. During a system power interruption, the power monitoring system detects the interruption and directs the PLD to backup content of the DRAM devices onto an on-board Flash, such as NAND. When power is restored, the contents of the Flash are transferred back into the DRAM with no loss of critical data. This is obviously inconveniently time-intensive. One of the typical applications of such devices is a very high performance low latency block storage device closely coupled to the CPU in servers and blades.
Limitations are also faced by other types of widely-employed memory, such as flash memory. Such limitations include long write or program times and memory management expenses in that the memory must first be erased before being re-programmed which will not make them suitable for these high performance applications. In summary, the current implementation is costly, not green, requires backup to non-volatile (NV) media during power interruption and restoration on subsequent power up.
The foregoing limitations, in addition to others known in the industry, has prompted using MRAM as an alternative form of storage of information. In fact, MRAM is widely expected to replace traditional memory in the near future. However, replacing memory such as DRAM or SRAM or even flash with MRAM, presents its own set of problems, one of which is meeting requisite timing requirements in a system using traditional memory. In other words, simply replacing traditional memory with MRAM cannot be done in a plug-and-play setting because MRAM is quite different and therefore has its own set of requirements. For example, the host (or central processing unit (CPU)) in a computer or storage system employing MRAM cannot readily access the MRAM.
Thus, there is a need for a high performance host-based system employing MRAM with reduced latency